Signal translating apparatus



y 1945. c. M. SINNETT 2,376,456

S IGNAL TRANSLATING APPARATUS Filed Oct. 9, 1941 2 Sheets-Sheet 1 y1945- C. M. SINNETT SIGNAL TRANSLATI'NG APPARATUS Filed Oct. 9, 1941 2Sheets-Sheet 2 10; 3nventor PatentedMay 22,1945 2,376,456

UNITED STATES PATENT OFFICE SIGNAL TRANSLATING ArPARA'rUs Chester M.Sinnett, Westmont, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application October 9, 1941, Serial No. 414,305

16 Claims. (01. ire-100.41) This invention relates to signal translatingapin the tuning circuit of a 40-50 megacycle oscilparatus, and moreparticularly to a signal translator, and when its capacity is varied,frequency lating device of the capacity type adapted for use shiftoccurs in the oscillator circuit and frequency especially in connectionwith phonograph records, modulation results. This may be passed througthe primary object of my invention being to prothe regular FM channel 0a radio receiver, for vide a capacity type pickup as aforesaid theexample.

capacity of which is varied in accordance with The movable electrodepreferably consists of a the record groove modulation to providefrerelatively thin, narrow, fle b Strip of metal quency modulation in anoscillator circuit wheretending across the stationa y ele trode a d inthe pickup constitutes a tuning element. anchored at its ends. Suitable'means are pro- More particularly, it is an object of my present videdfor tensioning the electrode whereby to coninvention to provide animproved capacity picktrol its natural period. The need e is P ra up asaforesaid the operating parts of which have secured to the movableelectrode substantially a low mechanical impedance and the needlepresway w n its ends, a m nt of t sure of which is very low on therecord whereby l5 electrode is confined substantially to a region toprovide long record and needle life, thereof in the vicinity of theneedle. This avoids Another object of my present invention i t vibrationreflections from other parts of the movprovide an improved pickup asabove set forth able electrode back toward the needle, thereby which hasgreat sensitivity and is operable over u stantially mina n di t rtionand xtenda much wider range than pickups of this type s the range vwhich h P up i p te heretofore known. with great efliciency. If desired,the fixed elec- A further object of my present invention is to ode maybe arranged for adjustment relative to provide an improved capacitypickup whi h will the movable electrode so as to control the normalafford a large gain in signal to noise ratio. ir can h r w n a d th s te s n i i y of Still another object of my invention is to prothe d ThePi up device s e t em y light vide an improved capacity type pickupwherein n Weight, having a needle p essure o approxithe natural periodof the vibrating electrode can t y 20 rams, or about two-thirds of anounce, be easily controlled. as compared with about three-and-a-half orfour A further object of my present invention i to ounces characteristicof the prior art pickups. provide an improved pickup as aforesaid whichAlso, since the movable electrode is light and flex- Will not cause therecord with which it is coible, t has a w e han cal impedance. This,operating during reproduction to radiate exombined With the light weightof the needle traneous sounds and which will not itself produce on therecord, affords long life to both records such sounds. and needle.

still a further object f my invention is to pro- The novel features thatI consider charactervide an improved pick-up as set forth above istic ofmy invention are set forth with particuwhich will operate with a minimumof distortion. arity in the app d c aimshe invention it- -It is also anobject of my present invention to self, however, both as to itsorganization and provide an improved pickup device of the charmethod ofoperation, together with additional Obacter et forth which i Verysimple, yet sturdy, 40 jects and advantages thereof, will best beunderin construction, hich i e o mic l i o t, stood from the followingdescription of several which is highly efficient in use, and which willem o iments thereof, when read in connection have a long life. with theaccompanying drawings, in which In accordance with this invention,Iprovide a u e 1 is a Side elevation of one form of suitable supportingmember which carries a pair p up constructed in accordance with my Dr ofelectrodes in capacitive relation to each other, t t on, the pi kup beinshown mounted one of the electrodes being stationary and the on asuitablesupporting arm shown partly in other being mounted for movementrelative to section,

the stationary electrode. The movable electrode Figure 2 is an invertedplan view of this form carries a needle adapted to cooperate with the ofmy invention, a

groove of the record. Due to the, wave shape Figure 3 is a sideelevation of a second form form in the record groove, the capacitybetween of my invention shown with its arm mounted the electrodes iscaused to vary in' accordance in operative position,

with the movements imparted to the needle by Figure 4 is an enlarged,top plan view of the the record groove. The pickup may be connectedpickup device of Figure 3,

Figure 5 is a side elevation thereof with certain parts in section,

Figure 6 is a bottom plan view thereof,

Figure 7 is an enlarged, bottom, perspective view thereof with certainparts broken away for the sake of clearness,

Figure 8 is an enlarged sectional view taken on the line VIII-VIII ofFigure 6,

Figure 9 is a wiring diagram illustrating one circuit in connection withwhich my improved pickup may be used advantageously and Figure 10 is aset of curves showing the resonance of the pickup arm of Figure 3 undervarious conditions.

Referring more particularly to the drawings,

, wherein similar reference characters designate corresponding partsthroughout, there is shown, in Fig. 1, a pickup arm I which carries onits free end a supporting block 3 recessed to provide a face 5 and apair of lugs or projections I and 9 which terminate in a plane beyondthe face 5. The block 3 is also formed with a slot H which substantiallyseparates the projection 9 from the body thereof. A screw l3, which isthreadedly received in the projection 9 and has its end bearing againstthe body of the block 3, as clearly shown in Fig. 2, is adjustable tomore or less separate the projection 9 from the body of the block for apurpose presently to be set forth.

The block 3 is also cut away centrally to receive a block of theinsulating material l5 which has its face flush with the face 5. Securedto one end of the block l5, as by a screw I1, is one end of a plate l9which may be made of copper, for example, and constitutes the stationaryelectrode of the capacitor. The movable electrode 2| is constituted by arelatively narrow, thin, flexible strip of nickel-steel alloy or anyother suitable material, having a thickness of about 3 mils and a widthof about 5 2 inch. The strip 2| extends across the lower part of thestationary electrode l9 and has its ends bent over the lugs orprojections I and 9 to which they are secured, whereby the electrode 2|is anchored in place. By adjusting the screw I3, it is obvious that thetension of the electrode 2| may be varied, and therefore its resonance,or natural period of vibration, controlled at will. The projections Iand 9 extend sufliciently beyond the stationary electrode iii to providean air gap 23 between the electrodes i9 and 2|, wherebythe twoelectrodes constitute a capacitor. If desired, any other suitabledielectric material may be interposed between the electrodes I9 and 2|instead of air, or, when they are spaced from each other by an air gap,they may each be coated with a thin layer of some suitable dielectricmaterial, such as zinc chromate. The normal width of the air gap 23 isof the order of three or four mils. However, a set screw 25, which isthreadedly received in the insulating block 15 and the end of whichbears against the lower end ofthe plate or stationary electrode i9, maybe adjusted to vary the width of the air gap so as to control thesensitivity of the pick-up.

Secured to the lower edge 2|a of the movable electrode 2| at a pointsubstantially midway between its ends is a needle 21 which is adapted tocooperate with the grooves of a phonograph record. The needle 21 has itsmajor portion extending in a plane substantially parallel to that of theelectrode 2| and terminates in a record engaging tiplla which may be ofsapphire or the like for long wear. portion of the needle is rigidtorsionally and is Preferably, the major wire or the like having adiameter of the order of 10 or 12 mils and having a length of about a to$43", its upwardly extending shank 21b being the portion by which it issecured to the electrode 2 I ,-asby solder 29 or the like.

'When the needle tip 21a tracks the groove of a record of the laterallyundulating type, the groove will cause the needle to movecorrespondingly, and since it is rigid in torsion, it will cause theflexible electrode 2| to move toward and away from the stationaryelectrode IE! to thereby vary the capacity of the capacitor. It' isdesirable to confine the movement of the movable electrode 2| to aregion substantially in the vicinity of the needle 21, such as theregion bounded approximately by the dotted line A and the lower edge 2|aof the electrode 2|, since this will prevent reflections of vibrationalmovements of the flexible electrode 2| between its opposed, free edges2m and 2|b. For this purpose, the edge 2|b may be made much stiffer thanthe lower ed e 2|a by bending a marginal portion thereof adjacent theedge 2") out of its plane to provide a stiffening flange 2 lo in a planesubstantially normal to the plane of the electrode 2|. If desired, ablock of damping material 3| may be secured to the block 3 and theflange 2|c, as shown in Fig. 1, to clamp the vibration of the upperportion of the movable electrode 2|;

A pickup device such as that described above may be employed to controlthe frequency of any tuned circuit and finds its particular applicationin modulating an oscillator in a phonograph reproducing circuit. By wayof example, the pickup device, as shown in Fig. 9, is connected withsuch an oscillator which comprises a suitable oscillator tube 33provided with an oscillator tuning-inductance 35, the pickup capacitancebeing shunted across the inductance 35 and connected therewith through ashielded cable which may be constituted, for example, by the groundedpickup arm I within which is a conductor 31 connected to the stationaryelectrode l9. The capacity of the shielded cable should be relativelylow with respect to that of the pickup |92|, arid it may bemaintainedconstant by passing the conductor 31 through'a plurality ofspacers 39 of damping material such as printers roll, Glyptal, Du PontViscaloid, etc., interposed between the conductor 31 and the pickup armI. The output circuit 4| of the oscillator tube 33 is provided with atuned circuit 43 which is tuned off resonance with respect to theoscillation steady state-or mid-frequency. The'variation of the,

capacity at the pick-up will cause the oscillation frequency to varyabove and below the normal frequency, that is, the mid-frequency,thereby resulting in a frequency modulated signal which is delivered toa suitable output circuit and may be utilized in any suitable mannenasto operate a loudspeaker or the like (not shown). This type of circuitis more particularly disclosed and claimed in my copending application,Serial No. 459,375, filed September 23, 1942, and assigned to RadioCorporation of America.

In Figs. 3 to 8, inclusive, I have shown a modification of my inventionwherein the supporting block 3 is constituted by an annular member whichis removably carried by a head 45 to which of set screws 41. The head 45is preferably secured to the pickup arm I by means of a pair of leafsprings 49 of phosphor bronze. or the like, which are secured to andextend from the head 45 in parallel relation. Thesprings 49 straddle theadJacent end of the pickup arm I and their opposite ends are secured toa pair of blocks 50 which are carried by the pickup arm. Preferably,although not necessarily, a pair of strips or blocks of damping materialwhich may be of the same nature as the damping blocks 39 abovedescribed, are secured to the springs 49 by a suitable adhesive 53. Thearm I is pivotally mounted on a horizontal pivot 55 which is formed onthe upper end of the yok 51 having a downwardly extending, vertical pinor post 59 received in a standard 6!. Thus, the arm I and itstranslating device are capable of movement both in horizontal andvertical directions relative to the record.

The curve X of Fig. 10 shows what the response of the system would be ifthe head 45 were coupled rigidly to the pickup arm I. When the springs49 alone are interposed betweenthe pickup head 45 and the arm I, theresonance of the system becomes that represented by the curve Y, fromwhich it will be seen that there is a fairly sharp peak at about 60cycles. By providing a damping strip 5| on each of the resonance of thesystem is changed to that shown by the curve Z, from which it will benoted that springs 49, the u there is a smaller peak at about 80 cycles,and

that at the extreme, low frequency end, the response drops way down.

The insulating block I5 is made substantially semi-cylindrical in theform of my invention shown in Figs. 3 to 8 and it is recessed slightlyto receive the stationary electrode l 9. The set screw 25 in thismodification extends down through the top of the insulating block I 5,as clearly shown in Figs. 5 to 8, for the purpose of enabling adjustmentof the air gap 23. The annular block 3 is formed with a groove 63 on itsbottom surface, as clearly shown in Figs. 6 and 7, and the movableelectrode 2| is secured to the block 3 within the groove 63, as bestshown in Fig. 7. The block 3 in this modification is also formed with aradial slot 65 corresponding to the slot ll of the first describedmodification of my invention, the screw l3 again serving to place themovable electrode 2| under more or less tension by expanding the annularblock, or increasing its diameter slightly.

Preferably, the movable electrode 2| of Figs. 3 to 8 is formed of a verynarrow, thin, strip of medium-hard phosphor bronze or any other suitablematerial, being. in fact, even narrower and thinner than thecorresponding strip of Figs. 1 and 2, and again having its free, opposededges 2 la and 2 lb extending across the stationary electrode I9. Inthis modification of my invention, the strip 2| may have a thickness ofabout 1 /2 mils and a width of about 1 6 inch.. The purpose of makingthe electrode 2| so narrow is to make overlapping portions of the twoelectrodes as small as possible consistent with the desired results. Theneedle 21 of this form of my invention extends entirely across the strip2| and terminates, as above, in the needle tip 21a beyond the lower edgeam of the movable electrode. The other end of the needle 21 extendsbeyond the upper edge Nb of the movable electrode and terminates in arelatively long shank 2111 which is secured to an anchoring block 61held in place on the annular supporting block 3, as by a screw 5 69,best shown in Fig. 8. This arrangement, like the flange 2|c of Figs. 1and 2, confines the upper position illustrated by the dotted lines ofFig. 8,

pivoting substantially about the adjacent, lower edge of the block 61 asa center. In such movement, it is obvious that the lower edge of theelectrode 2| must move a greater distance than a the upper edge 2")thereof. Furthermore, since the strip 2| is anchored at its ends, onlysubstantially the mid-portion thereof in the region where the needle 21is secured thereto (that is, the region bounded substantially by theedges 2 la and 2H) and the dotted linesA-A) will vibrate to anyappreciable extent and sufficient to cause an appreciable change incapacity of the capacitor unit. The operation of this form of myinvention is precisely like that of the first described form, but has aresponse up to between 25,000 and 30,000 cycles, whereas themodification of Figs. 1 and 2 has a response of only up to about 10,000to 12,000 cycles.

Although I have shown and described but two embodiments of my inventionit will be apparent to those skilled in the art that many othermodifications thereof, as well as changes in those described, arepossible without departing from the spirit of the invention. Therefore,I do not wish to be limited except insofar as is made necessary by theprior art and by the spirit of the appended claims.

I claim as my invention:

1. A phonograph record signal translating device comprising a pair ofcooperating electrodes spaced from each other by a dielectric andconstituting a capacitor, a needle carried by one of said electrodes andhaving a free end adapted to cooperate with a record, said needle beingunconfined for free movement between its said free end and its point ofattachment to said one electrode, said last named electrode-beingmounted for movement relative to the other of said electrodes inresponse to movements imparted to said needle by the record whereby tovary the capacitance of saidcapacitor, means confining the movement ofsaid movable electrode substantially to a region thereof in the vicinityof said needle, and means for placing said movable electrode under moreor less' tension whereby to vary the natural period thereof.

2. A phonograph record signal translating device comprising a pair ofcooperating electrodes space from each other by a dielectric andconstituting a capacitor, one of said electrodes comprising a thin,flexible member mounted for movement relative to the other of saidelectrodes, a needle carried by said first named electrodeand having afree end adapted to cooperate with a record to vibrate said'first namedelectrode in accordance with movements imparted. thereto by the recordand thereby to correspondingly vary the capacitance of said capacitor,said needle being unconfined for free movement between its said free endand its point of attachment to said movable electrode, means forconfining the vibratory movement of said first named electrodesubstantially to a region thereof in the vicinity of said needle, andmeans for placing said movable electrode under more or less tensionwhereby to vary the natural period thereof.

3. A phonograph record signal translating device -comprising a pair ofcooperating electrodes spaced from each other by a dielectric andconstituting a capacitor, one of said electrodes comprising a thin,flexible member mounted for movement relative to the other of saidelectrodes, a needle carried by said first named electrode adapted tocooperate with a record to vibrate said first named electrode inaccordance with movements imparted thereto by the record and thereby tocorrespondingly vary the capacitance of said capacitor, and meanscomprising a portion of said first named electrode for confining thevibratory movement thereof substantially to a region in the vicinity ofsaid needle.

4. A phonograph record signal translating device comprising a relativelyfixed and a relatively movable electrode, said electrodes being spacedfrom each other by a dielectric and constituting a capacitor, saidmovable electrode comprising a thin, flexible member including a pair ofopposed edges, a needle carried by said movable electrode adjacent oneof said edges, said needle being adapted to cooperate witha record tovibrate said first named electrode in accordance with movements impartedthereto by the record and thereby to correspondingly vary thecapacitance of said capacitor, and means for stiffening the other ofsaid edges whereby to render said movable electrode more freely movableadjacent its needle carrying edge than along said other edge.

5. A phonograph record signal translating device comprising a relativelyfixed and a relatively movable electrode, said electrodes [being spacedfrom each other by a dielectric and con stituting a capacitor, saidmovable electrode comprising athin, flexible member including a pair ofopposed edges, a needle carried by said movable electrode adjacent oneof said edges, said needle being adapted to cooperate with a record tovibrate said first named electrode in accordance with movements impartedthereto by the record and thereby to correspondingly vary thecapacitance of said capacitor, and means formed integrally with saidmovable electrode along the other of its said edges for stiffening saidother edge whereby to render said movable electrode more freely movableadjacent its needle carrying edge than along said other edge.

6. A phonograph record signal translating device comprising a relativelyfixed and a relatively movable electrode, said electrodes being spacedmaterial out of its plane along a marginal portion adjacent said otheredge.

8. A phonograph record signal translating device comprising a pair ofcooperating electrodes spaced from each other by a dielectric andconstituting a capacitor, one of said electrodes comprising a thin,flexible member mounted for movement relative to the other of saidelectrodes and including a pair of opposed, free edges, a needle carriedby said first named electrode adapted to cooperate with a record tovibrate said first named electrode in accordance with movements impartedthereto by the record and thereby to correspondingly vary thecapacitance of said capacitor, andmeans for s0 confining the movement ofsaid movable electrode in response to said needle that one of its saidedges will move to a greater extent than the other of its said edges.

9. A phonograph record signal translating device comprising a pair ofcooperating electrodes spaced from each other by .a dielectric andconstituting a capacitor, one of 'said electrodes comprising a thin,narrow, flexible strip mounted for.

movement relative to the other of said electrodes and including a pairof opposed, free edges, a needle carried by said movable electrodeadapted I to cooperate with a record to vibrate said movable from eachother by a dielectric and constitut n a capacitor, said movableelectrode comprising a thin, flexible member including a pair of opposededges, a needle carried by said movable electrode adjacent one of saidedges, said needle being adapted to cooperate with a record to vibratesa d first named electrode in accordance with movements imparted theretoby the recordand thereby to correspondingly vary the capacitance of saidcapacitor, and a flange on said movable electrode along the other of itssaid edges for stiffening said other edge whereby to render saidelectrode more freely movable adjacent its needle carrying edge thanalong said flanged edge.

'7. The invention set forth in cla m 6 characterized in that saidmovable electrode is formed of flat, sheet material, and characterizedfurther in that said flange is formed by bending said electrode inaccordance with movements imparted thereto by the record and thereby tocorrespondingly vary the capacitance of said capacitor, said needleextending across said movable electrode beyond said free edges thereofand terminating in a shank beyond one of said edges, and means anchoringsaid shank whereby said last named edge is confined against movement toa greater extent than the other of said edges in response to movement ofsaid needle.

10. In a phonograph record signal translating device, the combination ofa supporting member, a pair of cooperating electrodes carried by saidmember and having an air gap therebetween whereby to constitute acapacitor, one of said electrodes comprising a stationary plate and theother of said electrodes comprising a flexible strip movably mounted onsaid supporting member for movement toward and away from said stationaryelectrode and having a pair of opp0sed, free edges, a needle carried bysaid movable electrode for cooperation with a record to vibrate saidmovable electrode relative to said stationary electrode in accordancewith movements imparted thereto by the record and thereby tocorrespondingly vary the capacitance of said capacitor, and

said needle is secured to said strip substantially mid-way between itsends.

12. The invention set forth in claim 10 characterizedby the additionofmeans on said supporting member for placing said strip under more orless tension whereby to vary the natural period thereof.

13. The invention set forth in claim 10 characterized by the addition ofmeans on said supporting member for adjusting the position of said plateelectrode whereby to gap between said electrodes.

vary the normal air 14. The invention set forth in-claim 10characterized in that each of said electrodes is coated with adielectric material.

15. The invention set forth in claim 10 characterized in that saidconfining means is constituted by a flange formed on said strip along amarginal portion adjacent one of its edges.

16. The invention set forth in claim 10 characterized in that saidneedle extends across said strip beyond its said opposed edges, saidneedle terminating in a shank beyond one of said edges, andcharacterized further in that said confining means is constituted by ananchoring member on said supporting member to which said needle shank issecured.

CHESTER M. SINNETT.

